In recent years, lithium secondary batteries have been widely used as power supplies for electronic devices such as mobile telephones, notebook-size personal computers and the like, and also as power supplies for electric vehicles and for electric power storage, etc. These electronic devices and vehicles may be used in a broad temperature range, for example, at midsummer high temperatures or at frigid low temperatures, and are therefore required to have an improved cycle property in a broad temperature range.
A lithium secondary battery is mainly constituted of a positive electrode and a negative electrode containing a material capable of absorbing and releasing lithium, and a nonaqueous electrolytic solution containing a lithium salt and a nonaqueous solvent. As the nonaqueous solvent, used are carbonates such as ethylene carbonate (EC), propylene carbonate (PC), etc.
As the negative electrode, known are metal lithium, and metal compounds and carbon materials capable of absorbing and releasing lithium. In particular, lithium secondary batteries using a carbon material capable of absorbing and releasing lithium such as coke, artificial graphite, natural graphite or the like have been widely put into practical use.
It is known that, in the lithium secondary battery using a highly-crystalline carbon material such as artificial graphite, natural graphite or the like as the negative electrode material, the decomposed product or gas generated through reductive decomposition of the solvent in the nonaqueous electrolytic solution on the surface of the negative electrode during charging detracts from the electrochemical reaction favorable for the battery, therefore worsening the cycle property of the battery. Deposition of the decomposed product of the nonaqueous solvent interferes with smooth absorption and release of lithium by the negative electrode, and therefore, in particular, the cycle property at low temperatures may be thereby often worsened.
In addition, it is known that a lithium secondary battery using a lithium metal or its alloy, or a metal elemental substance such as tin, silicon or the like or its metal oxide as the negative electrode material may have a high initial battery capacity but its battery performance such as battery capacity and cycle property greatly worsens, since the micronized powdering of the material is promoted during cycles thereby bringing about accelerated reductive decomposition of the nonaqueous solvent, as compared with the negative electrode of a carbon material. In addition, the micronized powdering of the negative electrode material and the deposition of the decomposed product of the nonaqueous solvent may interfere with smooth absorption and release of lithium by the negative electrode, and therefore, in particular, the cycle property at low temperatures may be thereby often worsened.
On the other hand, it is known that, in a lithium secondary battery using, for example, LiCoO2, LiMn2O4, LiNiO2, LiFePO4 or the like as the positive electrode, when the nonaqueous solvent in the nonaqueous electrolytic solution is heated at a high temperature in the charged state, the decomposed product or gas thereby locally generated through partial oxidative decomposition in the interface between the positive electrode material and the nonaqueous electrolytic solution interferes with the electrochemical reaction favorable for the battery, and therefore the battery performance such as cycle property is thereby also worsened.
As in the above, the decomposed product or gas generated through decomposition of the nonaqueous electrolytic solution on the negative electrode or the positive electrode interferes with the movement of lithium ions or swells the battery, and the battery performance is thereby worsened. Despite the situation, electronic appliances equipped with lithium secondary batteries therein are offering more and more an increasing range of functions and are being in a stream of further increase in the power consumption. With that, the capacity of lithium secondary batteries is being much increased, and the space volume for the nonaqueous electrolytic solution in the battery is decreased by increasing the density of the electrode and by reducing the useless space volume in the battery. Accordingly, the situation is that even decomposition of only a small amount of the nonaqueous electrolytic solution may worsen the battery performance at low temperatures.
JP-A 11-162511 discloses a lithium secondary battery with a nonaqueous electrolytic solution, which contains a compound having an S—O bond as the organic solvent therein and in which the material of the collector for the positive electrode and the material of the part of the outer casing that is in contact with the electrolytic solution on the positive electrode side is a valve metal or its alloy. In the paragraph [0018] of the patent publication, a phenyl methanesulfonate compound as an example of the compound having an S—O bond is disclosed, and the battery capacity in the initial stage at 25° C. and the cycle property are shown; however, the cycle property is not sufficiently satisfactory.
As a lithium primary battery, for example, there is known a lithium primary battery comprising manganese dioxide or graphite fluoride as the positive electrode and a lithium metal as the negative electrode, and this is widely used as having a high energy density. It is desired to inhibit the increase in the internal resistance of the battery during long-term storage and to improve the discharge load characteristic thereof at room temperature or low temperatures.
Recently, further, as a novel power source for electric vehicles or hybrid electric vehicles, electric storage devices have been developed, for example, an electric double layer capacitor using activated carbon or the like as the electrode from the viewpoint of the output power density thereof, and a so-called hybrid capacitor comprising a combination of the electric storage principle of a lithium ion secondary battery and that of an electric double layer capacitor (both the capacity by lithium absorption and release and the electric double layer capacity are utilized) from the viewpoint of both the energy density and the output power density thereof; and it is desired to improve the characteristics, especially the low-temperature cycle property of these capacitors.